Land filtration: This method was preferred during summer when the weather conditions are hot and the land is dry to absorb wastewater quickly. It was used first in 1897. In this treatment approach, an exposed land is filled with sewage to a height of about 10 cm. While the solids are filtered to remain on the surface, the sewage soaks into the ground and streams out into the drain the released to Port Phillip Bay. The pollutants from the sewage are broken down by the bacteria in the soil while the nutrients are used by the grass to grow.
The land filtration process takes around three weeks and is carried out in phases (Jones, et. al pp.203-6). The land is flooded for two days and it takes around five days for the soil to absorb the sewage. After the paddock has dried, sheep and cattle can graze the grass for two weeks then the process begins again. Lagoon treatment: This treatment process was used first in 1936. They are suitable for the climate of high solar irradiation and growing season throughout the year. Tropical areas form an ideal climate for lagoons.
In this process, raw sewage is poured to an excavated large open basin on earth. The naturally degraded waste by bacteria, algae and another pathogenic organism is removed by aeration and sunlight exposure. The natural lagoons used initially and were low cost and used little or no chemical for the process. These lagoons have since been the lagoons have since been replaced by modern lagoons with the first modern lagoon being constructed in 1986. The old traditional treatment approaches had their shortcomings and new methods are currently being applied at Werribee and Carrum in sewage treatment.
Method of treatment currently used at Werribee, the recent improvements and why were they introduced Currently, the Werribee plant uses modern lagoons that are made up of 10 pools. Each of the pools has the capacity ton hold around 600 million litres of wastewater. The sewage is run on the ponds as the bacteria in the pond's breaks down the organic solids (Jones, et. al pp.206). The waste is made clearer as it goes through each pool. The sewage undergoes the following treatment process at Werribee: · The raw sewage from Melbourne enters the lagoon at Weribee · The shelters remove the smell and cut out the greenhouse emissions from the waste as methane is collected · The collected methane gas is recycled, generating electrical energy that powers aerators and other parts of the centre · The aerator dissolve oxygen into the wastewater · An activated sludge process re4moves nitrogen from the sewage · After around 30 to 35 days, the treated sewage in the lagoon can be recycled or released to Port Phillip Bay.
· The water used by the plant is recycled and delivered to various offsite clients who include the Hoppers Crossing pumping station in Melbourne and is also used for irrigation and on-site upkeep. There have been improvements to create the modern lagoon treatment plant at Werribee that has two ponds: the anaerobic pond which does not use oxygen and the aerobic pond which uses oxygen. The two processes create two different bacteria that break down the sewage waste. The anaerobic process has bacteria that consume the oxygen that breaks down the waste in the sewage.
The bacteria in an anaerobic process release strong pungent odors and greenhouse emissions that are hazardous. The improved ponds have shelters that capture and remove the pungent smell and greenhouse emissions that were prevalent in the old lagoons. The gases that are removed from biogas that produces electrical energy runs the facility (Jones, et. al pp.200-9). The oxygen that accumulates as the waste is treated is forced into the water by the aerators in the initial phase. The oxygen decreases the unpleasant smell as it goes through the rest of the ponds.
The treatment currently used at Carrum The waste treatment at Carrum uses a secondary standard which involves two phases of primary and secondary treatment.
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